reserve SAS for Semi_Affine_Space;
reserve a,a9,a1,a2,a3,a4,b,b9,c,c9,d,d9,d1,d2,o,p,p1,p2,q,r,r1,r2,s,x, y,t,z
  for Element of SAS;

theorem Th34:
  not o,a,c are_collinear & o,a,b are_collinear & o,c,d1
  are_collinear & o,c,d2 are_collinear & a,c // b,d1 & a,c // b,d2
implies d1=d2
by Th19;
